c-Si phototransistors with base junction depth around 4.0 mu m with its common emitter DC current gain h(FE) within 300-1100 had been well controlled by implanting base doping levels from 3 x 10(14) to 6 x 10(14) cm(-2), which is suitable in any conventional commercial photosensing application. According to the experimental results, the higher the base doses implanted, the lower and more stable is the DC current gain h(FE) obtained. The higher base implanting doping level results in reproducible and uniform wafers. The common emitter open base breakdown voltage BVCEO ranges from 35 V (for lightly doped base) to 140 V (for heavier doped base) under the test condition of I-CEO = 100 mu A, and the collector-emitter leakage current for base current I-B = 0. The open emitter breakdown voltage is within 40 V for lightly doped base, similar to 220 V for heavier doped base under I-CBO = 100 mu A and I-E = 0 A. The breakdown mechanism includes punch through and avalanche multiplication.